1. Field of the Invention
The invention relates to an elastic spectacle-frame hinge, and more particularly to a hinge which comprises two elements, a fixed element and a mobile element, which are connected to a front and to a side-piece of the frame respectively.
The two elements are articulated in relation to one another about an axis of rotation by a pivoting head on one of the elements, which head is inserted in a pivoting head on the other element, and by a link which is disposed inside two elements and passes successively through the pivoting heads.
2. Description of the Related Art
A hinge of this type is known, in particular, from Patent Application FR 2 698 121, which was published on May 20, 1994. The pivoting heads are spherical in shape and pivot about an imaginary axis passing through the centre of the two spheres.
The two hinge elements are perforated by an internal duct so as to permit the successive passage of a strand which is anchored in each duct by one end. The tensile force exerted by the fixed element on the mobile element is proportional to the deformation of the strand in the event of the latter being, by nature, elastic. If the strand is non-extensible, the tensile force is proportional to the deformation of a spring mounted between the mobile element and the point at which the strand is anchored.
When the side-piece of the frame is in the normal opening position, the strand extends parallel to the direction of axial alignment of the two elements, while at the same time being offset in relation to the axis of rotation on an outer side of the frame. xe2x80x9cOuterxe2x80x9d is understood to mean the region which is not contained between the front and the two side-pieces in the normal opening position. Conversely, the region contained between the front and the two side-pieces forms the inside of the frame.
When the frame is closed, the strand is offset progressively from one side to the other in relation to the axis of rotation. The tensile force generates a return torque which is cancelled when the middle fibre of the strand passes vertically across the axis of rotation. This results in a bistable effect which ought to endow the hinge with a closing position and a normal opening position which are stable.
It is found to be the case, however, that nothing permits the opposing of the tensile force in the normal opening position, in which the strand is straight. Being offset outwards in relation to the axis of rotation, the strand exerts, on the mobile element, a torque which leads to pivoting of the side-piece towards an extra opening position.
In other words, in the known hinge, although the bistable effect leads to a stable closing position, it seems to lead, on the other hand, not to a stable normal opening position, but in fact to a stable over-opening position. It is clear that a situation of this kind does not make the frame comfortable to use, and reduces its stability when worn.
One of the objects of the invention is to improve a type of elastic hinge by using a link to join together the elements connected to the front and side-piece, so as impart a stable character to the closing and normal opening positions, and an unstable character to the extra opening position.
To that end, the subject of the invention is an elastic spectacle-frame hinge comprising two hinge elements, a fixed element and a mobile element, which are connected to a front and to a side-piece of the frame respectively and are articulated in relation to one another about an axis of rotation by a pivoting head on one of the elements, which head is inserted in a pivoting head on the other element, and by a link which is successively accommodated in an internal duct in the two elements which opens into the pivoting heads and is offset, in relation to the axis of rotation, from an inner side to an outer side of the frame when the side-piece pivots, in relation to the front, from a closing position to a normal opening position, characterised in that each pivoting head possesses a stop at the mouth of the internal duct on the outer side of the frame, which stops form, as a result of complementarity of shape of one with the other, an interface for pivoting about a second axis of rotation, the link being disposed between the two axes of rotation when the side-piece is in the normal opening position.
When the side-piece is in the normal opening position, the two complementary stops make it possible to neutralise the torque that tends to make the side-piece pivot outwards into an over-opening position. In other words, the normal opening position is a stable position.
The stops are arranged, as a result of complementarity of shape at a pivoting interface, so as to enable the side-piece to pivot from the stable normal opening position to an extra outward opening position. In the course of over-opening, the pivoting heads move apart from one another and the male and female knuckles reduce their contact surface.
The stops are formed at the mouth of the duct on the outer side of the frame so that the link passing successively through the pivoting heads remains offset inwards in relation to the second axis of rotation. In this way, the tensile force of the link creates a torque for returning the side-piece that tends to oppose the pivoting of the latter into over-opening. This return torque is counterbalanced only when the pivoting heads are inserted in one another again and when the male knuckles are in contact with a guide surface connecting the two female knuckles, that is to say in the normal opening position. In other words, the over-opening position is unstable.